1. Field of the Invention
The present invention relates to a developer replenishment apparatus for supplying a developer to image forming apparatuses such as copying machines, facsimile machines and printers which form an electrostatic latent image on an image bearing member by an electrophotographic or electrostatic recording method or otherwise, and turns this electrostatic latent image into a visualized image (toner image) with the developer accommodated in a developing apparatus.
2. Related Background Art
In a conventional image forming apparatus, whether it uses a one-component developer or a two-component developer, when the development of electrostatic latent images brings down the quantity of the developer in the developing apparatus below its prescribed level, a developing apparatus 208 is replenished with a toner from a developer replenishment apparatus in which a developer for replenishment (toner) is stored, namely, a hopper 200, as in one example shown in FIG. 14 appended to the present application.
Usually, the hopper 200 is provided with a toner cartridge (first developer container) 201 for supplying new toner to a developing apparatus 208 and a buffer part (second developer container) 202 for storing the toner supplied from the toner cartridge 201. When the quantity of the toner in the buffer part 202 has decreased, a toner sensor (not shown) disposed in the buffer part 202 detects the toner shortage, and toner is supplied from the toner cartridge 201 to keep the quantity of the toner in the buffer part 202 constant.
The conventional buffer part 202 is often oblongly shaped. In the hopper 200 of this type, the toner supplied from the toner cartridge 201 drops by gravity into and accumulates in the buffer part 202, and is supplied to the developing apparatus 208 via a toner supply inlet 204 by the bottom face of the buffer part 202 and a conveyance screw 205 provided within a replenishment pipe 203 communicating with this bottom face.
However, this system of filling the buffer part 202 with toner by gravity is susceptible to bulk density variations of the toner in the buffer part 202 while the toner is accumulating in the buffer part 202, and this could invite fluctuations in the quantity of the toner supplied to the developing apparatus 208.
A proposed solution to this problem is to circulate the toner in a shallow buffer part as disclosed in Japanese Patent Application Laid-Open No. H03-2178789.
In this system, as shown in FIG. 15, after the toner is supplied from the toner cartridge to the toner supplying position 92 of the buffer part 202, the toner is evened up by being circulatively conveyed within the buffer part 202 by agitating screws 89a and 89b. The toner, which is then conveyed by a conveyance screw 89c to an opening 90, is further conveyed to the developing apparatus via a replenishment pipe (not shown). This system, since it can better suppress bulk density fluctuations within the buffer than the method of filling the buffer part by gravity, has an effect of reducing fluctuations in the quantity of toner supplied to the developing apparatus.
However, the hopper having the conventional buffer part to be filled with the toner by circulative conveyance involves the following problems.
In a color image forming apparatus, in order to suppress density variations of output images, fluctuations in the quantity of replenishment from the hopper to the developing apparatus have to be eliminated.
One of the means to achieve the purpose is the use of a less fluid toner, whose bulk density is not readily varied by external disturbance, such as a difference in environment or a state of being let stand for a long period. However, since the use of such a low-fluidity toner makes it impossible to even up the toner with agitating screws in the conventional circulative conveyance type buffer part at other times than when replenishing the developing apparatus with the toner, the heap of the toner will remain uncollapsed and build up in the toner replenishment position, sometimes blocking the toner flow.
Even if the toner flow is not blocked, it may be prevented from a position where it can be detected by the toner sensor with the consequence that erroneous emptiness of the toner cartridge may be detected even though there is some remaining toner in the cartridge.
Moreover, in spite of the use of the low-fluidity toner, the difference in bulk density between the toner replenishment position and elsewhere may become too large, rather inviting increased fluctuations of the quantity of replenishment.